My niece

My daughter Emma and my niece Sofia spend a lot of weekends together as my brother and his wife work a lot.
They are both 11 and have been really close since they were little. They are always in and out of the pool all the time.
Well this morning I was working in my office upstairs and when I got up to look out the window and see they were ok, I saw them kissing each other under the waterfall at the end of the pool. I figured they thought they couldn't be seen as it is pretty secluded but I could see them clear as day. It's shallow at that end and while I was watching them I saw my niece put her hand inside the bottom of my Emma's bathing suit. She was obviously feeling her up and Emma was enjoying it. Emma then put her hand in Sofia's bathing suit bottom and doing the same back. They were clearly having a great time fingering each other as I could tell from their faces. I didn't know if I should say anything or just ignore it but I just let it go,
After a while they got out of the pool and went running into the house. They got cold drinks for the kitchen and said they were going to Emma's room to watch TV as they were too hot. No shit. About 20 minutes later I could hear them making little crying noises and giggling. They were definitely at it again in her room. After an hour they came out and went back to the pool. I figure I'll just not say anything and they'll probably grow out of it.

I just caught my 11 year old daughter masturbating with a vibrator last night and I have no idea where she got it from.
She was making a lot of noise in her bedroom and I thought she was playing her video games when she should have been asleep since it was a school night. I went to her room to tell her to quit the game and go to bed but when I opened the door I saw she was sitting naked on her bed naked leaning against some pillows just going at it with the vibrator. The thing was a little bigger than my middle finger and she got it most of the way in herself. She was obviously in the middle of an orgasm because when I stormed in to find out WTF she was doing she has her eyes tight shut and her body was shaking. I just closed the door and left.

My niece is 10 and my daughter is almost a year older. They get along great and my niece spends a lot of time with us. They usually hang out in the basement as we have a big TV and my daughter has a playroom down there. They’re always watching TV or playing with their iPads.
Last weekend they were down there for hours and I was going down to ask them if they wanted to go out in the afternoon. Half way down the stairs, I hear my niece ask my daughter why her pussy looks so different from my daughters. I stopped in my tracks. From their conversation, I realized that they must be looking at each others naked bodies. They were talking about the difference between the color or their pussys and size of the lips. Then they were feeling one anothers boobs, not that either of them have much in that department yet. Then I hear my daughter saying how her pussy is getting “damp”. As I’m just standing there trying to figure out what to do, I realized they were now fingering one another and clearly enjoying the experience. Well I remember being that age and doing the same kind of thing, so I crept back up the stairs and quietly closed the door.

One time when my 10 year old niece was staying over, I left her and my son who was almost 11 alone in the house while I went over to a neighbors for a couple of hours. When I came back I could hear them talking in his bedroom. At first I thought they were just playing on the computer but then I hear him say “can I touch it” to which she replied “sure but only if you let me touch yours”. I was going to yell out that I was back but it just felt weird and I thought I’d scare the shit out of them so I just stayed quiet. Then I hear her say “wow it’s really hard” and then he asks her to keep sliding her hands up and down. He told her that she was getting wet between her legs and asked if he could put his finger inside. (What a gentleman). She said yes and that she liked doing that to herself. Then I heard a little scream. He says “Are you ok” and she says “yes just keep doing it and do it faster. Then she says “let me do it myself and you can watch” and told him “now you can play with yourself too”. They were really going to town when I heard her let out another little scream. She must have come. He says to her that he’s feeling weird but didn’t want to stop so she says “let me take over”. I figured that she must be jerking him off until he shouts out “stop stop stop”. The he says he’s feeling all weird. She says she feel it too. Then she says “we better get dressed because your dad will be back soon. I give it a few minutes and then quietly open the back door and slam it shut calling out Hey kids I’m back. Do you want anything? They both come running down the stairs saying they are fine. Yeah the really were fine I guess.

My niece was 10 and my son was 9 at the time. I saw them both naked in the basement. He had his finger in her pussy and she was jerking his cock. They didn't know I'd seen them so I just went back upstairs and left them to it. Didn't we all do shit like that as kids?

That's a very healthy attitude. Kudos to you for showing restraint.